Biological activities of synthetic analogs of halocidin, an antimicrobial peptide from the tunicate Halocynthia aurantium

Immune Enhancement Effects of Neutral Lipids, Glycolipids, Phospholipids from Halocynthia aurantium Tunic on RAW264.7 Macrophages

Fractionated lipids of Halocynthia aurantium (Pyuridae) have been demonstrated to possess anti-inflammatory properties. However, their modulatory properties have not been reported yet. Thus, the objective of this study was to determine immune enhancing effects of fractionated lipids from H. aurantium tunic on macrophage cells. The tunic of H. aurantium was used to isolate total lipids, which were then subsequently separated into neutral lipids, glycolipids, and phospholipids. RAW264.7 cells were stimulated with different concentrations (0.5, 1.0, 2.0, and 4.0%) of each fractionated lipid. Cytotoxicity, production of NO, expression levels of immune-associated genes, and signaling pathways were then determined. Neutral lipids and glycolipids significantly stimulated NO and PGE2 production and expression levels of IL-1β, IL-6, TNF-α, and COX-2 in a dose-dependent manner, while phospholipids ineffectively induced NO production and mRNA expression. Furthermore, it was found that both neutral lipids and glycolipids increased NF-κB p-65, p38, ERK1/2, and JNK phosphorylation, suggesting that these lipids might enhance immunity by activating NF-κB and MAPK signaling pathways. In addition, H. aurantium lipids-induced TNF-α expression was decreased by blocking MAPK or NF-κB signaling pathways. Phagocytic activity of RAW 264.7 cells was also significantly enhanced by neutral lipids and glycolipids. These results suggest that neutral lipids and glycolipids from H. aurantium tunic have potential as immune-enhancing materials.

Creation of Recombinant Biocontrol Agents by Genetic Programming of Yeast

Bacterial infections caused by antibiotic-resistant pathogens pose an extremely serious and elusive problem in healthcare. The discovery and targeted creation of new antibiotics are today among the most important public health issues. Antibiotics based on antimicrobial peptides (AMPs) are of particular interest due to their genetically encoded nature. A distinct advantage of most AMPs is their direct mechanism of action that is mediated by their membranolytic properties. The low rate of emergence of antibiotic resistance associated with the killing mechanism of action of AMPs attracts heightened attention to this field. Recombinant technologies enable the creation of genetically programmable AMP producers for large-scale generation of recombinant AMPs (rAMPs) or the creation of rAMP-producing biocontrol agents. The methylotrophic yeast Pichia pastoris was genetically modified for the secreted production of rAMP. Constitutive expression of the sequence encoding the mature AMP protegrin-1 provided the yeast strain that effectively inhibits the growth of target gram-positive and gram-negative bacteria. An antimicrobial effect was also observed in the microculture when a yeast rAMP producer and a reporter bacterium were co-encapsulated in droplets of microfluidic double emulsion. The heterologous production of rAMPs opens up new avenues for creating effective biocontrol agents and screening antimicrobial activity using ultrahigh-throughput technologies.

Anti-inflammatory effects of neutral lipids, glycolipids, phospholipids from Halocynthia aurantium tunic by suppressing the activation of NF-κB and MAPKs in LPS-stimulated RAW264.7 macrophages

Halocynthia aurantium is a marine organism that has been considered a promising source for bio-functional materials. Total lipids were extracted from H. aurantium tunic, and then they were separated into neutral lipids, glycolipids, and phospholipids. In the present study, fatty acid profiles of three lipids and their anti-inflammatory effects in RAW264.7 cells were investigated. Among the lipid classes, phospholipids showed the diversity of fatty acid constituents, compared with the glycolipids and neutral lipids. Three lipids contain different contents of fatty acids depending on the kinds of lipids. The most contents were saturated fatty acids (SFAs, 53–69% of the fatty acids) and monounsaturated fatty acids (MUFAs, 15–17% of fatty acids) and polyunsaturated fatty acids (PUFAs, 14–32% of fatty acids) are followed. H. aurantium lipids not only dose-dependently inhibited nitric oxide production but also reduced the expression of inflammatory cytokine genes such as TNF-α, IL-1β, and IL-6 in LPS-stimulated macrophages. It was also demonstrated that the expression of COX-2 was dose-dependently suppressed. Moreover, H. aurantium lipids decreased phosphorylation of NF-κB p-65, p38, ERK1/2, and JNK, suggesting that three lipids from H. aurantium tunic provide anti-inflammatory effects through NF-κB and MAPK signaling. These results indicate that H. aurantium is a potential source for anti-inflammation.

Dimerization of Antimicrobial Peptides: A Promising Strategy to Enhance Antimicrobial Peptide Activity

Antimicrobial resistance is a global health problem with strong social and economic impacts. The development of new antimicrobial agents is considered an urgent challenge. In this regard, Antimicrobial Peptides (AMPs) appear to be novel candidates to overcome this problem. The mechanism of action of AMPs involves intracellular targets and membrane disruption. Although the exact mechanism of action of AMPs remains controversial, most AMPs act through membrane disruption of the target cell. Several strategies have been used to improve AMP activity, such as peptide dimerization. In this review, we focus on AMP dimerization, showing many examples of dimerized peptides and their effects on biological activity. Although more studies are necessary to elucidate the relationship between peptide properties and the dimerization effect on antimicrobial activity, dimerization constitutes a promising strategy to improve the effectiveness of AMPs.

Antifungal Activity and Action Mechanism of Histatin 5-Halocidin Hybrid Peptides against Candida ssp

The candidacidal activity of histatin 5 is initiated through cell wall binding, followed by translocation and intracellular targeting, while the halocidin peptide exerts its activity by attacking the Candida cell membrane. To improve antimicrobial activities and to understand the killing mechanism of two peptides, six hybrid peptides were designed by conjugating histatin 5 and halocidin. A comparative approach was established to study the activity, salt tolerance, cell wall glucan binding assay, cytotoxicity, generation of ROS and killing kinetics. CD spectrometry was conducted to evaluate secondary structures of these hybrid peptides. Furthermore the cellular localization of hybrid peptides was investigated by confocal fluorescence microscopy. Of the six hybrid congeners, di-PH2, di-WP2 and HHP1 had stronger activities than other hybrid peptides against all tested Candida strains. The MIC values of these peptides were 1–2, 2–4 and 2–4 μg/ml, respectively. Moreover, none of the hybrid peptides was cytotoxic in the hemolytic assay and cell-based cytotoxicity assay. Confocal laser microscopy showed that di-PH2 and HHP1 were translocated into cytoplasm whereas di-WP2 was accumulated on surface of C. albicans to exert their candidacidal activity. All translocated peptides (Hst 5, P113, di-PH2) were capable of generating intracellular ROS except HHP1. Additionally, the KFH residues at C-terminal end of these peptides were assumed for core sequence for active translocation.

Haloganan: a novel antimicrobial peptide for treatmentof wound infections

HG1 is a Leu-rich antimicrobial peptide (AMP). Previously, the peptide was shown to lose its activity in human serum although it possessed potent and broad spectrum antimicrobial activity against a wide range of pathogenic microbes. In an attempt to design an HG1 isomer that can overcome the problem of HG1, a structure–activity relationship study was conducted by substitution of each of five Leu residues with a Gln residue. Each substitute was tested for its antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) or Candida strains. In addition, the antimicrobial activity of HG1 isomers was examined in the presence of glycosaminoglycans or lipid components occurring in the extracellular matrix, human serum and wound fluid. As a result, it was determined that the third residue (Leu) in the sequence of HG1 was mainly responsible for abrogation of its antimicrobial activity in human serum or wound fluid. An HG1 isomer (L3Q) with a Gln-3 substitution exhibited a potent antibacterial activity in 50% human serum. While the anti-MRSA activity of L3Q was equivalent to that of HG1, its anti-Candida activity was found to be substantially reduced. In order to improve anti-Candida activity of L3Q, its cationicity was enhanced by replacement of the C-terminal Ala-19 with a Lys residue. Overall, an HG1 isomer with two substitutions of Gln-3 and Lys-19, named haloganan, was verified to have an advantage over HG1 in that it exerted its potent antimicrobial activity under conditions containing human serum and/or wound fluid.

Influence of Dimerization of Lipopeptide Laur-Orn-Orn-Cys-NH2 and an N-terminal Peptide of Human Lactoferricin on Biological Activity

Lactoferrin (LF) is a naturally occurring antimicrobial peptide that is cleaved by pepsin to lactoferricin (LFcin). LFcin has an enhanced antimicrobial activity as compared to that of LF. Recently several hetero- and homodimeric antimicrobial peptides stabilized by a single disulfide bond linking linear polypeptide chains have been discovered. We have demonstrated that the S–S bond heterodimerization of lipopeptide Laur-Orn-Orn-Cys–NH₂ (peptide III) and the synthetic N-terminal peptide of human lactoferricin (peptide I) yields a dimer (peptide V), which is almost as microbiologically active as the more active monomer and at the same time it is much less toxic. Furthermore, it has been found that the S–S bond homodimerization of both peptide I and peptide III did not affect antimicrobial and haemolytic activity of the compounds. The homo- and heterodimerization of peptides I and III resulted in either reduction or loss of antifungal activity. This work suggests that heterodimerization of antimicrobial lipopeptides via intermolecular disulfide bond might be a powerful modification deserving consideration in the design of antimicrobial peptides.

Anticancer activity of a synthetic peptide derived from harmoniasin, an antibacterial peptide from the ladybug Harmonia axyridis

Harmoniasin is a defensin-like antimicrobial peptide identified from the ladybug Harmonia axyridis. Among the synthetic homodimer peptide analogues derived from harmoniasin, HaA4 has been found to have antibacterial activity without hemolytic activity. In this study, we investigated whether HaA4 has anticancer activity against human leukemia cell lines such as U937 and Jurkat cells. HaA4 manifested cytotoxicity and decreased the cell viability of U937 and Jurkat cells in MTS assay and LDH release assay. We found that HaA4 induced apoptotic and necrotic cell death of the leukemia cells using flow cytometric analysis, acridine orange/ethidium bromide staining and nucleosomal fragmentation of genomic DNA. Activation of caspase-7 and -9 and fragmentation of poly (ADP-ribose) polymerase was detected in the HaA4-treated leukemia cells, suggesting induction of a caspase-dependent apoptosis pathway by HaA4. Caspase-dependent apoptosis was further confirmed by reversal of the HaA4-induced viability reduction by treatment of Z-VAD-FMK, a pan-caspase inhibitor. In conclusion, HaA4 caused necrosis and caspase-dependent apoptosis in both U937 and Jurkat leukemia cells, which suggests potential utility of HaA4 as a cancer therapeutic agent.

Therapeutic efficacy of halocidin-derived peptide HG1 in a mouse model of Candida albicans oral infection

OBJECTIVES

HG1 is an antimicrobial peptide derived from halocidin, which is naturally found in tunicates. The purpose of this study was to evaluate the therapeutic potential of HG1 as a novel antifungal agent for treating oral candidiasis.

METHODS

The pharmacokinetic properties of HG1 were explored in mice, which were orally administered a single dose of HG1. Anti-Candida activity of HG1 was investigated in a time-dependent manner in the presence of saliva obtained from healthy donors or patients with oral candidiasis. In addition, HG1 was evaluated for its anti-Candida activity in the presence of proteins extracted from the culture supernatant of Candida albicans. The therapeutic potential in vivo and ex vivo of HG1 against oral candidiasis was investigated using a mouse model of oral candidiasis.

RESULTS

Our data showed that absorption of HG1 into the blood did not occur following oral administration. In addition, HG1 exerted marked anti-Candida activity after short-term incubation at a concentration of 20 mg/L and it also caused a considerable reduction in fungal burden in the oral candidiasis mouse model when treated with 1 mg or 0.5 mg.

CONCLUSIONS

This study suggests that HG1, as a novel component of mouthwash, might become an alternative antifungal agent to conventional drugs used to manage oral candidiasis.

Effect of salt on the interaction of Hal18 with lipid membranes

One of the major obstacles in the development of new antimicrobial peptides as novel antibiotics is salt sensitivity. Hal18, an α-helical subunit of Halocidin isolated from Halocynthia aurantium, has been previously shown to maintain its antimicrobial activity in high salt conditions. The α-helicity of Hal18 in the presence and absence of salt was demonstrated by circular dichroism spectroscopy, which showed that the peptide was mainly unordered containing β-strands and β-turns. However, in the presence of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylserine (DMPS) vesicles, Hal18 folded to form α-helices (circa 42 %). Furthermore, the structure was not significantly affected by pH or the presence of metal ions. These data were supported by monolayer results showing Hal18 induced stable surface pressure changes in monolayers composed of DMPC (5 mN m(-1)) and DMPS (8.5 mN m(-1)), which again were not effected by the presence of metal ions or pH. It is proposed that the hydrophobic groove within its molecular architecture enables the peptide to form stable associations with lipid membranes. The balance of hydrophobicity along the Hal18 long axis would also support oblique orientation of the peptide at the membrane interface. Hence, this model of membrane interaction would enable the peptide to penetrate deep into the membrane. This concept is supported by lysis data. Overall, it would appear that this peptide is a potential candidate for future AMP design for use in high salt environments.

Antimicrobial peptides from marine invertebrates: challenges and perspectives in marine antimicrobial peptide discovery

The emergence of pathogenic bacteria resistance to conventional antibiotics calls for an increased focus on the purification and characterization of antimicrobials with new mechanisms of actions. Antimicrobial peptides are promising candidates, because their initial interaction with microbes is through binding to lipids. The interference with such a fundamental cell structure is assumed to hamper resistance development. In the present review we discuss antimicrobial peptides isolated from marine invertebrates, emphasizing the isolation and activity of these natural antibiotics. The marine environment is relatively poorly explored in terms of potential pharmaceuticals, and it contains a tremendous species diversity which evolved in close proximity to microorganisms. As invertebrates rely purely on innate immunity, including antimicrobial peptides, to combat infectious agents, it is believed that immune effectors from these animals are efficient and rapid inhibitors of microbial growth.

Therapeutic efficacy of halocidin-derived peptide HG1 in a mouse model of surgical wound infection with methicillin-resistant Staphylococcus aureus

We evaluated the therapeutic potential of HG1, an antimicrobial peptide, as a novel topical antibiotic by the use of a mouse surgical wound model of infection with methicillin-resistant Staphylococcus aureus. First, we attempted to determine whether or not HG1 infiltrated into the dermis when topically administered. Second, we evaluated the antibiotic effects of HG1 on skin infection via bacterial-enumeration and microscopic analyses. The results showed that topically administered HG1 was capable of penetrating into the dermis at the infection site, where it exerted its antimicrobial effects.

Antibacterials from the sea

The ocean contains a host of macroscopic life in a great microbial soup. Unlike the terrestrial environment, an aqueous environment provides perpetual propinquity and blurs spatial distinctions. Marine organisms are under a persistent threat of infection by resident pathogenic microbes including bacteria, and in response they have engineered complex organic compounds with antibacterial activity from a diverse set of biological precursors. The diluting effect of the ocean drives the construction of potent molecules that are stable to harsh salty conditions. Members of each class of metabolite-ribosomal and non-ribosomal peptides, alkaloids, polyketides, and terpenes-have been shown to exhibit antibacterial activity. The sophistication and diversity of these metabolites points to the ingenuity and flexibility of biosynthetic processes in Nature. Compared with their terrestrial counterparts, antibacterial marine natural products have received much less attention. Thus, a concerted effort to discover new antibacterials from marine sources has the potential to contribute significantly to the treatment of the ever increasing drug-resistant infectious diseases.

Multivalent Antimicrobial Peptides as Therapeutics: Design Principles and Structural Diversities

This review highlights the design principles, progress and advantages attributed to the structural diversity associated with both natural and synthetic multivalent antimicrobial peptides (AMPs). Natural homo- or hetero-dimers of AMPs linked by intermolecular disulfide bonds existed in the animal kingdom, but the multivalency strategy has been adopted to create synthetic branched or polymeric AMPs that do not exist in nature. The multivalent strategy for the design of multivalent AMPs provides advantages to overcome the challenges faced in clinical applications of AMPs, such as: stability, efficiency, toxicity, maintenance of activity in high salt concentrations and under physiological conditions, and importantly overcoming bacterial resistance which is currently a leading health problem in the world. The multivalency strategy is valuable for moving multivalent AMPs toward clinical applications.

Di-K19Hc, an antimicrobial peptide as new ototopical agent for treatment of otitis media

CONCLUSION

Di-K19Hc is a promising new ototopical antibiotic for treatment of middle ear infections associated with antibiotic-resistant bacteria.

OBJECTIVES

Di-K19Hc was previously shown to exert profound antimicrobial activity against a variety of antibiotic-resistant bacteria and fungi. In this study, we evaluated the potential use of di-K19Hc as a topical agent for the treatment of otitis media (OM) caused by a variety of microbial pathogens including bacteria resistant to conventional antibiotics.

METHODS

Antimicrobial activity of di-K19Hc was measured by colony count assay. Hearing threshold was determined by measurement of auditory brainstem response in mice treated with di-K19Hc. Mice treated with gentamicin were used as a control.

RESULTS

Di-K19Hc showed much stronger antimicrobial activity against methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa associated with human OM than did ofloxacin. Also, it was shown that the peptide exhibited substantial dose-dependent antimicrobial activity against microbes from middle ear fluid of patients with OM. Topically applied di-K19Hc caused neither a decrease of hearing level nor loss of hair cells.

Antimicrobial activity of a halocidin-derived peptide resistant to attacks by proteases

Cationic antimicrobial peptides (AMPs) have attracted a great deal of interest as a promising candidate for a novel class of antibiotics that might effectively treat recalcitrant infections caused by a variety of microbes that are resistant to currently available drugs. However, the AMPs are inherently limited in that they are inevitably susceptible to attacks by proteases generated by human and pathogenic microbes; this vulnerability severely hinders their pharmaceutical use in human therapeutic protocols. In this study, we report that a halocidin-derived AMP, designated HG1, was found to be resistant to proteolytic degradation. As a result of its unique structural features, HG1 proved capable of preserving its antimicrobial activity after incubation with trypsin, chymotrypsin, and human matrix metalloprotease 7 (MMP-7). Additionally, HG1 was observed to exhibit profound antimicrobial activity in the presence of fluid from human skin wounds or proteins extracted from the culture supernatants of Staphylococcus aureus and Pseudomonas aeruginosa. Greater understanding of the structural motifs of HG1 required for its protease resistance might provide feasible ways to solve the problems intrinsic to the development of an AMP-based antibiotic.

Structural features of distinctin affecting peptide biological and biochemical properties

The antimicrobial peptide distinctin consists of two peptide chains linked by a disulfide bridge; it presents a peculiar fold in water resulting from noncovalent dimerization of two heterodimeric molecules. To investigate the contribution of each peptide chain and the S-S bond to distinctin biochemical properties, different monomeric and homodimeric peptide analogues were synthesized and comparatively evaluated with respect to the native molecule. Our experiments demonstrate that the simultaneous occurrence of both peptide chains and the disulfide bond is essential for the formation of the quaternary structure of distinctin in aqueous media, able to resist protease action. In contrast, distinctin and monomeric and homodimeric analogues exhibited comparable antimicrobial activities, suggesting only a partial contribution of the S-S bond to peptide killing effectiveness. Relative bactericidal properties paralleled liposome permeabilization results, definitively demonstrating that microbial membranes are the main target of distinctin activity. Various biophysical experiments performed in membrane-mimicking media, before and after peptide addition, provided information about peptide secondary structure, lipid bilayer organization, and lipid-peptide orientation with respect to membrane surface. These data were instrumental in the generation of putative models of peptide-lipid supramolecular pore complexes.

Antimicrobial effect of halocidin-derived peptide in a mouse model of Listeria infection

Halocidin is an antimicrobial peptide found in the tunicate. A series of experiments were previously conducted in an attempt to develop a novel antibiotic derived from halocidin, as the peptide was determined to evidence profound antimicrobial activity against a variety of antibiotic-resistant microbes, with significantly less toxicity to human blood cells. In this study, we assessed the validity of one of the halocidin congeners, called Khal, as a new antibiotic for the treatment of systemic bacterial infections. Our in vitro antimicrobial tests showed that the MICs of Khal against several gram-positive bacteria were below 16 microg/ml in the presence of salt. We also determined that Khal retained sufficient target selectivity to discern microbial and human blood cells and was therefore capable of efficiently killing invading pathogens. Furthermore, Khal caused no aggregation problems upon incubation with human serum and also proved to be resistant to proteolysis by enzymes occurring in human serum. In the following experiments conducted with a mouse model of Listeria monocytogenes infection, we demonstrated that a single intravenous inoculation with Khal resulted in significant therapeutic effects on the survival of mice. In addition, our bacterial-enumeration analysis showed that after Listeria infection, livers and spleens from Khal-treated mice generated a great deal fewer recoverable CFU. Finally, the antibiotic effects of Khal were evaluated under confocal microscopy after we immunostained the liver sections with anti-Khal antibody. It was concluded that Khal bound specifically to the surfaces of bacteria colonized in the mouse liver and killed the bacteria rapidly.

Antifungal activity of synthetic peptide derived from halocidin, antimicrobial peptide from the tunicate,Halocynthia aurantium

Halocidin is an antimicrobial peptide isolated from the hemocytes of the tunicate. Among the several known synthetic halocidin analogues, di-K19Hc has been previously confirmed to have the most profound antibacterial activity against antibiotic-resistant bacteria. This peptide has been considered to be an effective candidate for the development of a new type of antibiotic. In this study, we have assessed the antifungal activity of di-K19Hc, against a panel of fungi including several strains of Aspergillus and Candida. As a result, we determined that the MICs of di-K19Hc against six Candida albicans and two Aspergillus species were below 4 and 16 microg/ml, respectively, thereby indicating that di-K19Hc may be appropriate for the treatment of several fungal diseases. We also conducted an investigation into di-K19Hc's mode of action against Candida albicans. Our colony count assay showed that di-K19Hc killed C. albicans within 30s. Di-K19Hc bound to the surface of C. albicans via a specific interaction with beta-1,3-glucan, which is one of fungal cell wall components. Di-K19Hc also induced the formation of ion channels within the membrane of C. albicans, and eventually observed cell death, which was confirmed via measurements of the K+ released from C. albicans cells which had been treated with di-K19Hc, as well as by monitoring of the uptake of propidium iodide into the C. albicans cells. This membrane-attacking quality of di-K19Hc was also visualized via confocal laser and scanning electron microscopy.

cDNA cloning of halocidin and a new antimicrobial peptide derived from the N-terminus of Ci-META4

Halocidin is an antimicrobial peptide, which is isolated from hemocytes from the tunicate, Halocynthiaaurantium. In this study, we cloned the full-length cDNA of halocidin from pharyngeal tissue, using a combination of RT-PCR and 5'-RACE-PCR. The observed cDNA structure indicated that halocidin is synthesized as a 10.37 kDa prepropeptide. Based on the cDNA structure and the known amino acid sequence of the mature peptide, it was concluded that the precursor of halocidin contains a 21-residue signal peptide, followed by the 18 residues of the mature peptide, and a 56-residue anionic C-terminal extension, which is removed later on in the process. The signal sequence of halocidin exhibited a high degree of similarity with the corresponding portion of the Ci-META4 protein, which had been previously discovered in the coelomic cells of another tunicate, Cionaintestinalis, and is considered to play a role in metamorphosis. However, in several respects, the cDNA structure of Ci-META4 suggested that it might constitute a precursor for an antimicrobial peptide. Thus, we prepared a synthetic peptide, which was comprised of 19 N-terminal amino acid residues in the predicted mature region of Ci-META4, and tested it with regard to its antimicrobial activity. As a result, we confirmed that the synthetic peptide exhibited potent antimicrobial activity against Gram (+) and (-) bacteria, while evidencing no hemolytic activity toward human erythrocytes.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.